From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Wrong results from in_range() tests with infinite offset
In-reply-to: 
 <CAEZATCVQO1vUXo0PjHToxvyZ8piwH-u-mTMqMhrGku2dYMhWbw@mail.gmail.com>
References: <3393130.1594925893@sss.pgh.pa.us>
 <3464257.1594936216@sss.pgh.pa.us>
 <CAEZATCVXfxCR+2gCSwFMQPfyFUVNzY7U6oHfCfjD1OCCVfWUiQ@mail.gmail.com>
 <3506768.1594947597@sss.pgh.pa.us>
 <CAEZATCVQO1vUXo0PjHToxvyZ8piwH-u-mTMqMhrGku2dYMhWbw@mail.gmail.com>
Comments: In-reply-to Dean Rasheed <dean.a.rasheed@gmail.com>
	message dated "Sat, 18 Jul 2020 09:16:39 +0100"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <3941232.1595081173.1@sss.pgh.pa.us>
Date: Sat, 18 Jul 2020 10:06:13 -0400
Message-ID: <3941233.1595081173@sss.pgh.pa.us>
Precedence: bulk

Dean Rasheed <dean.a.rasheed@gmail.com> writes:
>     if (isinf(base) && isinf(offset))
>     {
>         if ((base > 0 && sub) || (base < 0 && !sub))
>             PG_RETURN_BOOL(true);
>     }

Yeah, I'd experimented with more-or-less that logic before arriving at
my v2 patch.  I didn't like the outcome that "inf both infinitely precedes
and infinitely follows itself".  Still, it is nicely simple.

To make sense of this behavior, you have to argue that +/-inf are not
in any way concrete values, but represent some sort of infinite ranges;
then there could be some members of the class "inf" that infinitely
precede other members.  I thought that was bending the mathematical
concept a bit too far.  However, this isn't an area of math that I've
studied in any detail, so maybe it's a standard interpretation.

Still, I think the results my v2 patch gets make more sense than these.

			regards, tom lane